1. Field of the Invention
The present invention relates to an ignition distributor for an internal combustion engine and more particularly for minimizing radiation of radio-noise from the engine.
2. Prior Art
FIG. 3 shows the essential part of a prior art ignition distributor for an internal combustion engine disclosed by Japanese Patent Publication No. 61-38351. At the center of the bottom of a distributing rotor 1, a recess 1a is formed for fitting the end portion of a shaft S which rotates in synchronism with the internal combustion engine. The top of a rotor electrode 2 is covered with a dielectric plate 4 except the portion which a center carbon 3 abuts. The underside of the rotor electrode 2 is covered by a dielectric plate 5. The rotor electrode 2 and the dielectric plates 4, 5 are integrally secured to the distributing rotor 1 by means of a rivet 6, and rotate about an axis A of the shaft S. As many side electrodes 7 as there are cylinders are disposed circumferentially with a gap of a predetermined size between the tip end 2a of the rotor electrode 2, and are held in a unitary construction together with the center carbon 3 by means of an insulating distributing cap.
With the above-described construction, when the distributing rotor 1 is driven into rotation by the rotation of the internal combustion engine, a high voltage generated by an ignition coil (not shown) is distributed to a corresponding ignition plug through the rotor electrode 2 and the side electrode 7. At this time, a spark discharge is produced due to the gap between the rotor electrode 2 and the side electrode 7, being a source of radio-noise. The dielectric plates 4, 5 serve to minimize the radio-noise.
FIG. 4 shows another prior art ignition distributor in which silicone varnish 40, for example, is applied as a dielectric material over the entire surface of the tip end 2a of the rotor electrode 2.
Although the above-described prior art ignition distributors play a role in minimizing radio-noise, the distributor shown in FIG. 3 suffers from a problem in that the increased number of parts and a time-taking consuming assembly process make the distributor more expensive. The distributor shown in FIG. 4 suffers from a drawback in that the surface to which the silicone varnish 40 is applied tends to be gradually worn out thus causing a non-uniform discharge over the entire surface of the tip 2a of the rotor electrode opposite to the side electrode 7. The non-uniform discharge causes the distributor to exhibit unstable discharge characteristics and increased radio-noise.